This invention pertains to a band saw, in particular for workpieces made of rock and similar materials that are difficult to cut, with a workpiece table on which at least one workpiece can be fixed, and a tool support for a continuous band saw blade.
Band saws can be used to saw various types of materials. For a large percentage of materials to be sawed, the types of band saws used are those in which a continuous saw blade penetrates into a workpiece by an advancing motion. Thereby, a straight cut arises in the workpiece.
When sawing workpieces made of stone and similar materials that are difficult to cut, these common band saws have been proven to be unsuitable since the contact length of the band saw blade in the workpiece and the resultant forces are too great.
In order to reduce the contact length of the band saw blade, the purely translational motion made by the saw blade with respect to the workpiece must be combined with a tilt motion. This produces a curved, in particular arc-shaped cut in the workpiece.
In DE 31 02 766, a metal sawing machine is described which is used to cut through a workpiece as it produces a rocking motion of the saw blade. In this application the machine is a horizontal band saw, by which an arc-shaped cut can be produced while maintaining a constant contact length in the workpiece. The arc-shaped cut is thereby permanently prescribed in its geometric dimensions. The curved fixed pattern is generated by two geometric formed parts, called cams. These cams must be manufactured in an expensive manner according to the desired cut in the workpiece. It is thus not possible to vary the geometric parameters of the arc-shaped cut without having to expend a considerable amount of effort to manufacture special geometric formed parts. With the fixed pattern of the cut, the contact length in the workpiece is also automatically fixed. Thus it is not possible to adjust the contact length of the band saw blade to the geometric dimensions of the workpiece, the hardness of the material of the workpieces, i.e. the material quality of the workpiece, much less optimize it.
The object of this invention is to provide a band saw that makes it possible to saw materials, in particular workpieces made of stone that are difficult to cut. This band saw is intended to be used for workpieces of different geometric dimensions and different material properties, in particular different material hardnesses. The band saw according to the invention is characterized by a high cutting capacity, simple handling and cost effective production. Furthermore, it is fast and flexible to use, without having to make significant changes to it.
This object is met according to the invention in that the workpiece and the band saw blade make translational motions and tilting motions relative to one another about an axis perpendicular to the cutting plane. These motions are coordinated with one another such that a crooked cut arises in the workpiece with the geometric parameters of the cut being continuously varied.
According to the invention the band saw can be provided with different setups. In general, the workpiece is fixed and the saw makes the translational motions and tilting motions about an axis perpendicular to the cutting plane. This is frequently advantageous when the workpiece is an especially heavy and large one.
On the other hand, it is, in principal, also possible for the tool support holding the band saw blade to be fixed, and the translational motions and the tilting motions are made by the workpiece table which holds the workpiece. This could prove to be advantageous if the tool support and the band saw are especially heavy and unwieldy.
A third possibility of relative movement between band saw blade and workpiece with respect to one another is to split up the translational motion and the tilting motion. It would be posssible, for example, for the workpiece to make the tilt motion in this case and the band saw blade to make the translational motion, or vice versa.
In the band saw according to the invention, band saw blade and workpiece can be arranged differently with respect to one another. Thus, for example, the device can be provided as a horizontal band saw or a vertical band saw.
In the band saw according to the invention, the translational motions and the tilting motions are coordinated between workpiece and band saw blade. An especially favorable embodiment of the band saw is to coordinate the motion sequences using an electronic control system. To this end, for example, the desired motion sequences can be calculated using a PC, the control signals can then be issued from it to corresponding servomotors to execute the motion sequences. In this manner, it is possible to arbitrarily coordinate the motion sequences with respect to one another.
The translational motions are composed of motion sequences of the band saw blade relative to the workpiece that are into and away from the workpiece. During the sawing process, therefore, an approach and withdrawal of the band saw blade with respect to the workpiece takes place in an alternating fashion in the translational motion sequence. These motions are exactly coordinated with the tilt motion.
An advancing motion in the direction toward the workpiece can be superimposed onto the translational forward and backward motions of the band saw blade relative to the workpiece during the sawing process. These advancing motions can be implemented in various ways. For one thing, it possible that a continuous advancing motion is superimposed onto the translational and tilt motion sequences during the entire sawing process. Furthermore, it is also conceivable for the advancing motion, i.e. the approach between workpiece and band saw blade, to occur discontinuously during the sawing process. In this case, the approach of workpiece and band saw blade occurs in shifts. In other words, workpiece and band saw blade first approach one another in one advancing motion, then the combination sawing process including translational and tilting motions occurs, after which another shift approach between the band saw blade and workpiece takes place.
Depending on whether a continuous advancing motion or a discontinuous advancing motion is combined with the translational and tilting motions, the outline of the cutting path changes.
The cut that results in the workpiece that arises during the process, i.e. the edge of the cutting plane on the material, has a crooked shape in the band saw according to the invention. Depending on how the motion sequences, i.e. translational motion, tilt motion and advancing motion, are combined with one another, the cut is made in the workpiece accordingly. The crooked cut can, for example be in the shape of an arc. In individual cases, it may be especially favorable to have an arc of a circle cut result from the sawing process. To produce a circular cut, it has proven advantageous if the tilt axis lies at approximately half the height (for a vertical band saw) or at approximately half the width (for a horizontal band saw) of the workpiece, i.e. approximately near its line of symmetry.
By combining translational and tilting motions, the contact length of the band saw blade, i.e. the point of contact of the band saw blade, can be tailored to the workpiece for the sawing process. In general, the contact length of the band saw blade remains nearly constant in the workpiece during the sawing process. For special requirements it is possible to vary the contact length during the cutting process. This can then be an advantage if the material to be sawed is inhomogeneous, i.e. has areas of differing properties such as different material hardnesses.
In the limiting case, the contact length of the band saw blade can be just a single point on the workpiece.
There are many criteria according to which the coordination of the motion sequences is set up to produce a desired curved cut and to select the optimal contact length of the band saw blade in the workpiece. For one thing, the geometric dimensions of the workpiece, i.e. the height, width and depth as well as the external contour of the workpiece must be taken into account. Furthermore, a very important factor is the material properties of the material to be sawed. In this regard, the material hardness plays a particularly important role.